Generally, a technique for embedding data in material to the effect that the embedded data is perceptible or imperceptible in the material is referred to as watermarking. Code words are applied to copies of material items for the purpose of identifying the copy of the material item or for conveying data represented by the code words. In some applications, watermarking can provide, therefore, a facility for identifying a particular copy of the material.
A process in which information is embedded in material for the purpose of identifying a specific copy of the material is referred to as finger printing. A code word, which identifies the material, is combined with the material in such a way that, as far as possible, the code word is imperceptible in the material As such, if the material is copied or used in a way, which is inconsistent with the wishes of the owner, distributor or other rights holder of the material, the material copy can be identified from the code word and take appropriate action.
In co-pending UK patent application number 0327854.6 an encoding data processor is disclosed for application to for example digital cinema in which payload data having two or more fields is represented by watermarking an image with one or more code words. Each value of a first field of a payload data word is associated with a first code word, and each value of a second or subsequent data field is represented by a second code word, which is selected in dependence upon the value of the first data field. As such a detected code word can be used to identify one of a plurality of sub-sets into which the data words are divided, each data word in the sub-set having the same value in the first field. A second or subsequent field of the data word from the sub-set can be then identified by detecting a second code word from the material item. The second code word identifies a value in the second data field as well as the value of the first data field.
The first and second fields can be assigned to different associated parameters such as for example address parameters. The first field could therefore identify the country of distribution of the material, whereas the second field could identify a particular distribution outlet within the country. The second field may additionally identify information in the first or indeed any other field or fields. A watermarking system can be formed for identifying a point of distribution of copies of video material. However, for applications such as digital cinema it is desirable to reduce a likelihood of an embedded code word causing any perceivable degradation of the image. An example of a technique for reducing the likelihood of any perceivable degradation of a marked image is disclosed in an article entitled “A Watermarking Scheme for Digital Cinema,” by Jaap Haitsma and Ton Kalker, published in Proceedings of the International Conference on Image Processing,” KIP 2001, Thessaloniki, Greece, Oct. 7 to 10, 2001. In this published article there is disclosed a technique for watermarking an image for digital cinema, in which the mean luminance of every frame is modified in the temporal axis only. Furthermore, an amount by which the luminance of a pixel is change to embed a watermark code word is adapted in dependence upon a local scaling factor. The local scaling factor is determined for every pixel in accordance with whether an area surrounding the pixel is a moving texture area or a non-moving flat area.